The luminescent property of 2D perovskite materials promotes their applications in light emitting diodes, phosphor powders, and scintillators. Recently, an interesting extrinsic low-energy broadband luminescence is hotly investigated. However, the understanding of such emissions is still at the early stage. In this study, based on a modified solvent evaporation method, centimeter-size (BDA)PbI 4 (BDA = NH 3 C 4 H 8 NH 3 2+ ) single crystals are grown which, besides the band–band emission, show a large Stokes-shifted broadband luminescence. We find such emission can be effectively excited by sub-gap photons and conclude defects-induced shallow traps are the corresponding luminescence centers. Density functional theory (DFT) calculations indicate that in-plane iodine vacancies can introduce shallow electron traps in the band gap and give rise to the broadband emission.
Nannan Bi,Lei Zhang,Qiang Zheng,Fei Zhuge,Jiupeng Li,Xuan P.A. Gao,Juan Du
A vapor deposition method was applied to synthesize zinc oxide (ZnO) nanowires and nanorods with diameter from 40 nm to 500 nm, length from 1 μm to 70 μm by adjusting the flow rate of argon, oxygen and the pressure during growth. Results of scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM) proved the hexagonal wurtzite structure of the synthesized ZnO nanowires or nanorods , which grow along the <0001> direction. The results show that the growth conditions strongly impact the morphology, growth rate and optical properties of the ZnO nanostructures . The ZnO nanowires with small diameters tend to show stronger ultraviolet (UV) light emission from the electron-hole recombination near band edge in photoluminescence (PL), while those with larger diameters tend to exhibit PL spectra dominated by the broad green light emission due to the defects.
Xi Xiaonan,Li Yuanyuan,Liang Tianyuan,Wu Huaxin,Miao Ruonan,Gu Chao,Fan Jiyang
The semiconductor–metal heteronanocrystals (HNCs) that possess a perfect epitaxial interface can accommodate novel and interesting physical phenomena owing to the strong interaction and coupling between the semiconductor excitons and metal plasmons at the interface. Here, we fabricate the pyramidal ZnO–Au HNCs and study their unique photophysical properties. Several Au nanospheres are perfectly epitaxially bound with a single ZnO NC owing to the small lattice mismatch between them and there are also ZnO–Au–ZnO sandwiched HNCs. There is a strong coupling between the green defect-associated recombination in the ZnO NC and the localized surface plasmon resonance (LSPR) of the Au nanosphere at the interface of the HNC. This leads to resonant defect recombination–LSPR energy transfer and resultant nearly complete quenching of the green defect luminescence of the ZnO NCs in the HNCs, leaving only the UV exciton luminescence. The lifetimes of both the green and UV emission bands decrease significantly in the ZnO–Au HNCs relative to that of the pure ZnO NCs owing to the combined effect of resonance energy transfer and surface plasmon enhanced radiative transition. The exponent of the luminescence intensity–excitation intensity power function for the green emission band is remarkably smaller than unity, and this suggests that the involved defects have an intermediate concentration.
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